Add vibe.utils.meta.typetuple

Collection of extensions to std.typetuple that either has not been
merged yet or can't make it into Phobos for some reason.
Add framework for attaching functions as attributes
Fix unit test. See #344.
vibe.http.rest cleanup : example + URL

Change DDOC example for registerRestInterface into documented unit-test, reformat it for better readability.
Add method for URLRouter to check registered routes.
Implement standard way for URL formatting using stand-alone function
rest example: add termination event
rest example: add unittests to verify route paths